City Public Advocate Letitia James spent almost all of her more than $750,000 in taxpayer matching funds against an underfunded GOP opponent, meaning little or nothing will be returned to government coffers.

City Public Advocate Letitia James burned through nearly all of the more than $750,000 in taxpayer matching funds in a lopsided race against a poorly funded opponent — spending $500,000 on a single Election Day expenditure, public records show.

James, a Democrat who cruised to reelection over Republican political consultant J.C. Polanco, spent about $1.7 million in total on the race, according to filings with the Campaign Finance Board. She crushed Polanco, her nearest competitor — earning 812,234 votes to his 172,601.

James was widely expected to win her reelection bid — but still filed a statement of need requesting the entire amount of matching funds, citing Polanco as a strong opponent. In doing so, she noted media coverage about the would-be pol — including stories about how little money he had raised.

Candidates are required to return matching funds they do not spend on their race — but James has just $39,018 left in her coffers, meaning the taxpayers will get back little, if anything.

James spent a whopping half-million in one day — Nov. 7, the date of the general election, when she reported the $500,000 payment to Global Strategies Group. Her campaign said the payment was for digital ads that appeared on social media sites, community and ethnic newspaper sites and other news sites — including the Daily News website.

Filing the expense on Election Day meant that it did not have to be reported within 24 hours, as all expenses in the 14 days leading up to the election must. Instead, it became public last week, after a postelection filing deadline. The campaign said it paid the bill as soon as it received it, and didn’t control when the bill came.

If James had not spent down her cash by Election Day, it would have been more difficult to spend — while candidates can pay election-related expenses after the race, those payments are subject to more scrutiny from the Campaign Finance Board.

“Public Advocate James has long championed public campaign financing, so that holding public office is accessible regardless of wealth,” a campaign spokesman said. “She proudly ran a campaign fueled by thousands of small dollar donors from across New York City, and is honored she was reelected for a second term.”

James raised $949,274 in private funds to qualify for $756,486 in matching cash. In the leadup to qualifying for the match, she received thousands in donations from members of her staff, The News previously reported.

Polanco raised $26,391 in his bid. He did not qualify for matching funds.

City Controller Scott Stringer did not accept matching funds in his reelection bid. Both Mayor de Blasio and Republican Nicole Malliotakis accepted — and spent — matching funds.

Queens Borough President Melinda Katz, also a Democrat who cruised to reelection, was the only incumbent beep to file a statement of need — raising $980,912 and taking in $567,464 in matching funds. She spent a good chunk of her public dollars — leaving her with a balance of $168,819 that she’ll have to return, minus any postelection expenses she reports.

Other beep incumbents facing long-shot challengers opted to receive a smaller portion of their match — and, in two cases, have so much cash in their coffers they are likely to return all of it.

Bronx Borough President Ruben Diaz Jr., for example, raised about $1.4 million in private funds and received $406,397 in matching funds. Because he has a balance of $869,687 in his coffers, he’ll almost certainly have to return his full match.

Staten Island Borough President James Oddo raised $129,044 in contributions and took in $215,044 in public funds; after spending around $190,000 on the race he’ll be returning more than $150,000 to the Campaign Finance Board.

Manhattan Borough President Gale Brewer, another shoo-in for reelection, raised $115,028 and accepted $209,334 in matching funds — but with a balance of $133,825, much of it will likely be returned.

But Brewer’s campaign appears to have been delinquent in filing disclosures regarding expenses in the days leading up to the general election, when they must be reported daily. An Oct. 26 bill for $65,523.86 wasn’t reported until Nov. 21; an additional $31,530.20 spent on Nov. 1 was reported on Nov. 28.

“Because we ran a scaled-back campaign without a full-time compliance staffer, we didn’t get the paperwork we needed together as quickly as we wanted. We regret the delay,” spokeswoman Jessica Mates said.